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Wednesday, 14 December 2011

Embodied cognition is not what you think it is. But I do understand why people think differently; it's because of the depressingly endless stream of papers published in Psychological Science that claim to have found that body posture somehow influences the contents of some cognition about the world. The latest "exciting" new finding claims that estimates of magnitude (size, amount, etc) are affected by your posture. The paper is well summarised at the Guardian for those without access to the paper (UPDATE: I am also talking to Rolf Zwaan, lead author of this paper, in the comments section there.)

It's a terrible paper, so it's apparently time for another in what might have to become a more frequent series, In which I am a bit rude about a rubbish paper and worry about how to kill papers like it. At the end, I've also talked a little about the role science journalism plays in maintaining the momentum for papers like this, via their own version of the file drawer problem. I'd be interested in people's thoughts.

The claim
Eerland, Guadalupe & Zwaan (2011) tested the hypothesis that we mentally represent magnitudes as a number line (Restle, 1970). This line runs from left to right; smaller numbers are to the left, larger numbers to the right. The suggestion was that leaning to the left should make smaller numbers more readily accessible, while leaning to the right should make larger numbers easier to call to mind; a priming effect. They tested this by manipulating posture while people made estimates of the magnitude of a bunch of things.

The questions were designed to be things people didn't know the exact answer to, but that they could generate a non-random estimate for. Example questions are "What is the height of the Eiffel tower in meters?", "How many people live in Antwerp?" and "What is the average life expectancy of a parrot in years?". While people were generating their estimates, they stood on a Wii Balance Board which tracked their centre-of-pressure (a measure of posture). They were instructed to stand 'upright', and to do this the data from the balance board was presented to them as a dot on a screen with a target - a computer warned them if their posture slipped away from the target. The mapping from posture to the screen was manipulated without participant's knowledge, so that in order to keep the dot on the target people were actually leaning left or right or were upright (varying by about 2%).

The question was whether this postural manipulation had any effect on estimates of magnitude. The questions all entailed different scales with different units (e.g. metres vs kilos), so to make the data comparable the authors z-transformed the results. This is a standard transformation; a z-score is equal to (data point - the mean)/the standard deviation, and the numbers that come out are unitless; they can be directly compared. Experiment 2 was the same design as Experiment 1 but all the questions had answers that ranged from 1-10 and participants knew their answer had to fit this range.

In both experiments, there was only a main effect of Posture, and comparisons revealed that leaning left made estimates smaller than standing upright or leaning right, but that leaning right was not different from standing upright. The authors conclude they have supported their hypothesis and that posture influences estimation of magnitude in accordance with the mental number line theory.

Why this is all entirely wrong
Where to begin? First, and I really can't seem to emphasise this enough, this is not embodied cognition. Second, the experimental question itself is ill-posed - at no point do the authors ask 'what is the function of magnitude estimation? What's it for?'. If we estimate magnitudes in order to actually do things in the real world, and these estimates are so fragile that they can be nudged by a 2% variation in posture, we would never be able to achieve our goals that depend on these magnitudes. So the paper itself is theoretically incoherent, yet another victim of psychology's lack of a central theory. Third, Restle's (1970) paper is not about magnitude estimation - it's about how people do fast addition of numbers. In addition, it claims that the mental number line is very fuzzy, with large regions being treated as the same; this is relevant to the discussion below about power and effect sizes.

But, just like the 'moving through time' paper (Miles, Nind & Macrae, 2010) the real disaster area is the experiment itself. If I had reviewed the paper, it would have gone something like this:

1. The hypothesis was clearly written once the data were in
The authors say 'We hypothesized that people would make smaller estimates when they leaned slightly to the left than they would when they leaned slightly to the right." (pg. 1511). They make no reference to the idea that leaning left and right relative to upright should produce different results, which is clearly implied by the mental number line theory.

2. The data don't actually support the mental number line theory
Leaning left produced smaller magnitude estimates on average across all questions and participants, but leaning right did not differ from upright. There's nothing in a mental number line that should make the left pull on behaviour harder than the right.

3. Handedness doesn't explain this
The authors do try to explain this asymmetry by saying that all their participants were right handedand there is evidence that "when people attempt to balance themselves, they show a subtle directional bias favoring whichever hip is on the same side as their dominant hand (Balasubramaniam & Turvey, 2000)" (pg. 1513). In essence, they claim that 'upright' for a right hander is actually slightly right of actual upright.

The reason this doesn't explain their results is that they utterly fail to test this. They recorded centre-of-pressure data, but do not analyse it at all and so they have no evidence of an actual shift. If they did have evidence of such a shift, they should have run a control condition where they identified each person's 'upright' position and calibrated 'left' and 'right' relative to that baseline (and a real journal would have demanded that they run this experiment; resolving a confound requires data, not a half-hearted citation). Actually, in the Methods, they mention calibrating the balance board for each participant, so either they calibrated it the way I just suggested (thus ruling out their handedness explanation) or they calibrated something else and it's not clear from the paper. Regardless, they don't get to call on handedness.

(A side note: if this handedness bias exists in their data, and if the lean influences magnitude estimates, then the bias is the only reason they found the effect to the left; it increased the size of the experimental manipulation to the point where it could be seen in the data. So even if the author's theoretical claims are true, this manipulation check suggests they were very lucky to see anything because they didn't manipulate posture enough).

4. There is no postural data in this paper
The authors report no data to support their manipulation of posture. Posture involves sway - we bipeds are dynamically unstable (like upright pendulums) and postural control is an active process of error correction. The authors report that the manipulation moved the centre-of-pressure by about 2%; but this will be on average, and given that the postural control system wants to keep you actually upright, there will have been plenty of sway back towards being in line with the pull of gravity. This time series of sway data should then have been indexed so that you knew which way people were swaying when you asked them the question.

As it stands, we have no way to evaluate how successful their postural manipulation was (which, given the manipulation failed in one direction, is critical information) nor what posture was actually up to when they answered the questions (which, given the next point, seems fairly crucial to me as well).

5. Many of the questions do not show the effect
The Supplementary data reports the median response for each question and sway condition. Only 25 of the 39 questions have larger numbers in the right sway condition compared to the left sway condition; only 9 show a pattern of increasing magnitude from left to right when you include the upright condition. The authors clearly got lucky in finding their result, suggesting the odds of replicating the effect are low.

6. The effect sizes are tiny
Backing up that last claim, I looked at the effect sizes. The authors report η2 which is effectively 'proportion of variance explained by the effect'. The effect sizes ranged from 0.07 - 0.17; 7-17% of the variance was explained by the posture manipulation. These effect sizes are very small (in my experiments with 8-10 people I typically see effect sizes around .7 or .8). In other words, the statistical trend that enabled the main effect of posture to become statistically significant is very, very small, and only the large amount of data is allowing sufficient power to find it. This type of tiny effect is fairly common in psychology (hence the typical large n's in psychology research) but it makes many of us worry about statistical vs actual significance.

Summary
This paper is not an example of embodied cognition, and worse, there are methodological and analysis flaws throughout the paper that make the data fairly uninterpretable. But, just like Miles et al (2010) this effect is now in the literature and in the popular press and there's no obvious way to kill it. Replication is unlikely to work, and even if it did, snazzy journals like Psychological Science don't like publishing mere replications (or,worse, failures to replicate). These high-impact journals publish exciting results that never get looked at again and thus are never corrected in the literature; it's a serious problem with real consequences (e.g. Diederik Stapel's fraudulent work showed up in many of these high impact journals and was never subjected to the replication attempts which would have revealed the fraud).

A note to science journalists
The popular coverage of papers like this, and the general lack of interest in follow-up on the internet, helps make these ideas spread and never get corrected. The problems with this paper, however, are mostly the kind of thing you spot when you're a scientist with experience with the literature and the analyses. Science journalists typically do not have this expertise; their job tends to make them less specialised, so they tend to lack the specialist knowledge and broader context that makes these papers stick out like a sore thumb to a reader like me. I'm not passing judgement on this lack of specialisation - it makes perfect sense and it allows them to engage with a broader audience than I will ever attract. That's their job, and that's fine.

But what I would love would be if running their analysis past an interested scientist became more standard. We have our biases and foibles so you'd have to be able to take all the advice with a grain of salt and with one eye on the different goals of science and science journalism. In this age of 'research impact', where we are heavily evaluated on our ability to see our work have consequences beyond the 20 people who read our journal article, I'm willing to bet you could find plenty of people happy to give a paper and a write-up a once over and you could take our advice or not. Maybe this just runs into the various problems with peer review, and I'm depressingly aware that it would be fairly easy to get glowing reviews on this paper, for example (clearly they've already had a couple via Psych Science). But as we try to develop a sustainable and sustained research programme centred on our theoretical approach, these results create noise we have to fight through, and I am personally very keen to address these issues in front of a wider audience.

Another issue is science journalism's version of the file drawer problem. The big science blogs all write positive write-ups of the exciting news, because that's what they're trying to communicate. But not writing a more critical piece on something that's getting a lot of attention creates the same bias as not publishing failures to replicate. I wrote this post in part because no-one else was going to; science journalists, do you have room to ever do this kind of work? One good example may be the 'arsenic life' story, although that was still kicked off by a scientist who happened to blog; so maybe there is a use for us after all!

27 comments:

In the discussion around Stapel, on the social cognition facebook site, Brian Nosek brought up an open science project that he at that time was tentatively starting (and which I haven't looked too deeply into yet). But, the gist was that a whole bunch of groups take a paper from a high impact journal, just like psych science, get the materials from the original group, and try to replicate it. I think that would be really interesting (maybe tossing some graduate students on it as part of their training). But, the replication thing really needs to be addressed.

I've actually thought about doing replications of papers like this as, say, a lab practical for undergraduates - I'd get 130 students a year through a study, we could test some ideas about confounds, etc.

Having grad students around the world to work on programming displays, etc could be a great idea, because that would be the bottleneck; I could code up this experiment but I have other projects that take priority. But if we agree on using Matlab and the Psychtoolbox or something, and make the code available; then anyone with the right hardware can replicate the study.

That's a problem though, in many cases. In this study, you would need a lab equipped with a Wii and specialized Wii software - which I suspect most aren't.

And in the case of Stapel's work, many of the experiments would be a real hassle to replicate e.g. one involved going into a train station, collaring people and getting them to sit down on a series of chairs, with two confederates (white and black) - and the station had to be dirty on one experimental and clean on the other!

Of course he never actually did that, he just made it up. But even if he had, it would be such a hassle to replicate that no-one ever would...

I'm not trying to tar this paper with the same brush as Staple but you see the point. A study which anyone can replicate with Matlab and a few hour's work is much more likely to get replicated that one that requires special hardware or a 'field trip' out of the lab.

Brilliant post! Your points around the lack of postural data, sway, and handedness are spot on. Something else to think on: fix your eyes on a point, them move or tilt your head to the left. Your eyes move RIGHT - and down - with respect to your head (the same movement direction as reading from left to right). As you return your head to upright, your eyes move LEFT - and up - with respect to your head (the opposite of reading left to right). So even if one were to count as irrelevant the myriad variety of combinations of bodily organisations AND ENVIRONMENT -eg groundplane- which effect centre-of-pressure shift (which may or may not involve a lean or tilt to the head), postural sway (ie movement) is pretty..um..important. As is measuring eye movement.In any case, I have to ask: centre of what? Humans are highly articulated, dynamically unstable structures (as you point out) and not blocks of wood. Without measuring the relative positions and tilt of head-to-pelvis-to-gravity and groundplane for each participant, and checking that the same bodily organisational strategy was employed to achieve a shift in the centre-of-pressure by all participants, then you're not comparing apples with apples. I find it extraordinary that there was a check for handedness, but no measure of 'footedness' - the preferred standing leg. There are so many simple, accurate ways to measure this...and really, the only thing this experiment could have measured using only centre-of-pressure data was weight distribution preferentially to one leg or the other...

Thanks, Tony :) Someone has to talk about these papers, they make a big splash but are then never replicated or talked about ever again, except as evidence that we already know how embodiment works.

acturelab - thanks, and your points are all good! The counter rotation issue is interesting, because it comes up in the Miles et al paper too. They measured sway at the knee, and said when you thought about the future you swayed forward. Of course, when your knee sways forward your head sways back; so what the hell does that mean? :) It's a symptom of these people thinking the body is the simple bit, while the mental state is the cool bit. As someone who studies the body bit and knows how complex it is, this bugs the crap out of me :)

Neuroskeptic; point taken on hardware, but it just occurred to me that there are some bottlenecks like display and data analysis programming that could get solved with a little effort.

Hi Andrew,Just a thought I had regarding the two recent postural studies in Psyc Science; the studies claim some sort of dependence between postural performance and mental performance, and the authors interpret this from within an embodied cognition framework. The studies remind me of the work by Thomas Stoffregen; in a set of experiments he demonstrated that actors strategically modify their posture so as to optimize performance on a 'supra-postural' task (visual search), if I understand correctly.Could it be that certain body states (say, postural lean) facilitate performance on a mental task, and would that not be evidence in favor of embodiment?

I would have to say 'yes and no'. Tom's stuff is certainly relevant. However, Tom isn't showing that posture affects the performance of any internal mental state (he's pretty hard core ecological psych :) His work has demonstrated that we use posture adaptively to improve our access to information. This is a little different.

Take the visual search stuff. The basic paradigm, as I recall, is to put people in a moving room. These are four walls raised off the ground and able to be moved rhythmically with motors. The inside of the walls typically has nice clear optical texture. When people are standing in these rooms while the walls move, they couple their sway to the sway of the wall; when the wall comes towards them, they sway backwards and vice versa. This demonstrates the role of optic flow in maintaining an upright posture.

The work to which you refer entails having a 'dual task', where people have to look at a monitor and do a complex visual search task. Dual tasks are supposed to make your performance worse. What Tom found is that when the monitor is on the wall and moving, people remain coupled to that motion; when the monitor is on a stand and not moving, people stop being coupled to the room and reduce their sway - performance got 'better' in the dual task.

Tom interprets this sensibly as showing that postural sway is modifiable and used adaptively to aid current performance; the hard visual search task meant people reduced their sway to provide a more stable base of support for vision.

So...yes, I think Tom's work is relevant to discussions of embodied cognition (done properly). But no, it's not the same was what's proposed here. Posture is controlled so as to provide a stable base for perception of task relevant information. (What 'stable' is depends on the task, and there is no single metric that captures this; sometimes more sway is better, e.g. his recent work on sway and motion sickness).

A side note; I visited Tom's lab many years ago when he was still in Cincinnati and tried the moving room out. He pushed the room a lot while I was in it, and it felt like the optic flow was pulling my eyes out of my head :) Very cool!

Just to add to the list of problems.... There are plenty of cultures that write in the other direction. I would be bet that if you did a simple ordering task to see how Americans and Europeans ordered magnitudes, you would find that quite a few people in "our" culture more naturally think in the opposite direction or have no preference (e.g. simply give people a bunch of straws cut to different length, bottles of different sizes, etc., and see if they preferentially order from left to right). Further, even if you could establish a preference, it is probably fairly easy to manipulate with some simple priming paradigms (putting the right posters on the wall in the waiting room, etc.).

If I wanted to test this hypothesis with this type of experiment, I would have a manipulation of people's number-line preference, then I would confirm the preference through sorting tasks or other behavioral measures, and only then would I put them on the balance board. If you could show this effect, even at 7-17% of the variance and show that the directionality was reversible if you do a manipulation of numerical representation, you would have a start.

Of course, that is just to clean up the science. Even if all that could be demonstrated, it still would not have anything to do with Embodied Cognition.

Hi Andrew,Thanks for the reply!Regarding Thom's work, you said " His work has demonstrated that we use posture adaptively to improve our access to information."OK. But what if someone were to claim that leaning backward was done adaptively to improve access to information specifying events that occurred in the past? And that this information is somehow carried by (not necessarily represented in) the nervous system?John

Anonymous,The word "information" is used in a very particular way in the ecological approach. Tom's work shows that people have access to patterns of light when they move in particular ways, and that moving so as to reveal certain patterns improves the accuracy of behaviors. This is because the patterns in the light are specific to certain properties of environmental-structures-relative-to-the-organism.

I'm interested in what you think the term 'information' means in a claim such as "leaning backward improves access to information specifying past events". What is that 'information' and in what way does it 'specify'?

I've been following your exchange with the lead author on the Guardian site with mounting dismay. It's become increasingly obvious that they a) erroneously conflate centre of balance with 'leaning', b) may never have heard about let alone understand postural sway, and c) have not realised that eyes can move relative to the head (perhaps they should have looked at "Eye position predicts what number you have in mind"Loetscher, et al, doi:10.1016/j.cub.2010.01.015 ?) and d) refuse to understand how any of these might have anything to do with their study. An childish ad hominem retort about purported breach of nettiquette does not constitute a scientific or even a professional response - so it seems like your words have fallen on resolutely deaf ears. Cheers to you, though, for raising pointy details about human movement - like you it annoys the hell out of me that some folk think the 'body is the simple bit'. For a piece of research into human movement and cognition, tthey failed to observe...human movement. What they actually measured was (post hoc hypothesis) the statistical likelihood of a bunch of right handed people to underestimate a guessed figure while standing with weight distributed marginally more to the left and staring fixedly at a crosshair trying to keep it within a certain area by correcting postural sway (and possibly holding their breath what with all the concentration). Which has bugger all to do with leaning, mental number lines, or as far as I can tell, embodied cognition.I wish, really wish, that if researchers want to pursue research into embodied cognition but are not remotely interested in actually observing human movement, that they would bring someone into their team who has expertise in the area.

But what if someone were to claim that leaning backward was done adaptively to improve access to information specifying events that occurred in the past? And that this information is somehow carried by (not necessarily represented in) the nervous system?John, you've actually posed the question quite well. Like Eric, I'm intrigued by the idea of the 'information specifying past events'; it's not clear what that would look like in ecological terms (see below) but this isn't a crazy way to formalise the hypothesis to be more useful. I think that posing it well, though, makes a few objections to the idea clear.

Eric's covered my first point; perceptual information, in the ecological approach Tom advocates too, is created via a very specific process that relates to the physical structure of the thing the light is bouncing off, for instance.

The metaphor 'future is forwards' isn't this necessary kind of relationship. There's only a conventional reason why this metaphor holds; it could have been different. So at best, there's only an association between 'forward' and 'the future'. (In fact, Sabrina just found this article for me now, which discusses a language where the future is, indeed, behind people! Apparently it's often about vision; you can see the past (things in front of you) but not the future (things behind you). Then, many people treat time as a circle, rather than a line, while apparently the Chinese treat the future as 'up'). Presumably in these people you would find varying effects, if it were real.

So, what counts as 'forward'? In Miles et al, they measured sway at the knee; but when the knee moves forward the head moves back. So why is the mental representation of time associated with motion of the knee and not the head? Sway is simply more complex than it's ever suggested in these studies, and this matters.

Then (my main objection) the postural control system has essentially one function; to keep you upright. Tacking on a second function (swaying forward to enhance access to thoughts about the future) is a bad idea, because you're asking the system to move in a manner that has nothing to do with how close you currently are to falling over.

Note that your hypothesis is a different claim than the one Mile et al tested; they found thinking about the past lead to (tiny) swaying back, and vice versa. You'd need to demonstrate the causal link in the other direction, which, interestingly, is the direction that this 'leaning left' paper works in. They manipulated sway and showed effects on number estimation. If they had actual sway data to show the misestimations varied with actual sway, I'd have a weaker objection; I'd mostly be left questioning why such tiny effects would have any behavioural relevance. But given how variable the response data were, I'm willing to bet tying it to actual posture at the time of response would not help them.

So, to really test your hypothesis, you'd need 1) at least two cultural groups, with varying metaphors for time or number, 2) detailed sway data from a variety of sensors, 3) timestamped to when the questions were asked. If you get reliable effects of sway on judgements in all the right directions, then you'd have a stronger argument to make. I still bet it won't work; I think these two papers got lucky in their data. But that's not to say you couldn't test your clearer hypothesis!

Amen, acturelab! I agree entirely :) I've enjoyed having the argument on the Guardian site, though, because it's more public than these debates tend to be so maybe some people will see it. Those people are my target, not Zwaan; I'll never convince him, he's too invested.

In normal quiet unperturbed stance the body essentially behaves like a plank; from head to toe there is --I believe-- very little movement around the joints. Most of the body activity responsible for sway involves rotations around the ankle joint, supported by lower leg muscles. If we were to adopt a slightly squatted position by bending the knees, then this would have no effect on center of pressure, but it would lower the center of mass though. Conversely, if I were to stretch both my arms sideways at the same time, this would raise my center of mass somewhat (making my body more vulnerable to perturbations), but again it would hardly affect my lean. So yes, recording only knee position (as done in the time-travel study) is not ideal, but if we make the simplifying assumption that the rest of the body is more or less stiff, then to my mind this can be a valid approximation of lean.

Andrew said: "the postural control system wants to keep you actually upright". True, but if the support surface (enclosed by the feet) is large enough, we have little difficulty leaning in a particular direction. Unless this costs too much effort (e.g., muscle fatigue) or when we reach the stability margins, I believe there is considerable room for postural excursions. Moreover, this creates the opportunity for actors to use posture in the service of other tasks.

Andrew said: " Of course, when your knee sways forward your head sways back". I wonder whether this is always true: we could either squat, resulting in forward displacement of the knee, OR we could configure our body into a C-shape (which is presumably what Andrew has in mind), OR our whole body (head plus knees) leans forward, as long as this poses no difficulties.John

John,You are quite correct that it is not always the case that knee sway forward = head sway back. Andrew's bigger point, however, is that these studies didn't check. At any rate, which looks more natural:

Knee's forward with counter rotation at the hips to keep head upright Like This.

Head counter rotation to knee angle, as displayed in different directions here.

Or Keeping the body like a plank when the knees rotate forward, Like This. ;- )

By the way, for a happy medium, a body plank with a clear head-lean-back, this kid is pretty darn good.

Again, though, one big point is that teasing apart these different possibilities requires more sophisticated measures than either study presented. Totally apart from the viability of the hypothesis, this lack of proper measurement technique should have gotten the papers rejected.

Hi EricTrue, the studies didn't check, but my point is; how bad is that? The authors implicitly assumed (or perhaps they never even considered) that the body is more or less a plank. This to me sounds like the easiest bodily configuration, and there was no reason for the actors to engage in more complicated body postures. Personally, I wouldn't reject a paper purely on these grounds, but I fully agree that the studies are conceptually muddled.Great videos by the way! :-)John

Andrew, you wrote: "the postural control system has essentially one function; to keep you upright". Now, if I understand Tom correctly, we hardly ever stand upright for its own sake; standing upright is usually done in the service of another activity, such as exploring the environment, or having a conversation while standing in a bar. In such cases, posture is geared towards facilitating performance of other activities and improving access to information (eg., through exploration). Would it be a far-feched idea if we extend this idea toward performance on internal mental states?

I have no idea how that could work and how that could improve access to information. However, as you are well aware, information in the ecological sense can be carried in different physical mediums; optic patterns, acoustic patterns, haptic patterns, etc. Would it be conceivable that information can also be carried by neural patterns that are lawfully related to a state of affairs, and that as perceivers/actors we exploit these patterns to guide our actions? A particular neural pattern could be specific to a state of affairs in the past, and certain postural behaviors would then facilitiate access to that information. Perhaps this idea is complete nonsense, but I'd be curious to hear your ideas on this.John

Would it be conceivable that information can also be carried by neural patterns that are lawfully related to a state of affairs, and that as perceivers/actors we exploit these patterns to guide our actions? A particular neural pattern could be specific to a state of affairs in the past, and certain postural behaviors would then facilitiate access to that information. I need to digest this a little. While I'm doing that, let me say a) I don't think this is nonsense, and b) you should read this post by Sabrina where she suggests something very similar.

Very interesting, and not nonsense at all. Just crazy enough to work? Possibly! :)

Would it be conceivable that information can also be carried by neural patterns that are lawfully related to a state of affairs, and that as perceivers/actors we exploit these patterns to guide our actions?

I'm worried about this. I suspect the important concepts might be put together in a way that doesn't quite work. In particular, what would it mean for us to perceive our neural patterns, and use those patterns to guide our action?!? What is the mechanism that perceives a pattern of neurons? What uses that information to guide our action? I am fine with the idea that lawfully related neural patterns are necessary for proper perception-action linkages to occur (there are potential flaws even there, but it is a perfectly good hypothesis). However, we still need a better way to describe how such neural patterns help.

Sorry for the language nit-picking, I'm not trying to be a jerk. I really believe that many of the problems with brain-talk in psychology are about getting the language right in subtle ways.

Ah, timely articles. If we want evidence that there is plenty of variety in the directionality of how people represent their number lines, here is a pretty good review of studies looking at the direction of counting-with-fingers. The review looks at cross-cultural and developmental data. It is couched in a somewhat cliche nature-nurture context, but the overall messages that there is considerable variation, and that this variation can be predicted based on various factors, is well supported.

Hi John, you wrote: "True, the studies didn't check, but my point is; how bad is that? The authors implicitly assumed (or perhaps they never even considered) that the body is more or less a plank. This to me sounds like the easiest bodily configuration, and there was no reason for the actors to engage in more complicated body postures."

The problem is, to make the body behave like a plank is actually pretty hard work, because the structure is more like an asymmetrically loaded heavy ball (head) balanced on an articulated bendy stick (spine), which is supported on another heavy ball (pelvis), itself supported on two articulated -but less bendy- sticks. All sorts of perturbing forces act around the articulated bendy stick bit: circulation, respiration, peristalsis - just to name a few. I suspect that the tendency to locate postural sway at the ankles is because movement is more obviously observable there: one ‘side’ of the joint is fixed (the foot-on-the-floor) so the other ‘side’ (the lower leg) appears to move more. In standing, all the other joints of the body are free to move both ’sides’ – but in any case movement at the ankles is just as much a correcting response to perturbations higher up as it is a contributor to perturbations which ‘cause’ postural sway. All of which sounds (even to me as I write) like nit-picking but it is important in the light of two things: the head with its teleceptors and vestibular apparatus, and something else you wrote which interests me immensely:

"Would it be conceivable that information can also be carried by neural patterns that are lawfully related to a state of affairs, and that as perceivers/actors we exploit these patterns to guide our actions? A particular neural pattern could be specific to a state of affairs in the past, and certain postural behaviors would then facilitiate access to that information."

If we assume that the body is a plank, then leaning means the head also leans. That is, one leans with respect to horizon and gravity. Tilting the visual and vestibular systems like this is going to evoke a righting reflex – which one has to override in order to maintain the lean. Perhaps, just perhaps, this could affect number estimation because it’s a ‘specific’ (ie not normal) state of affairs?

If we let the body be articulated, then it is possible to change the centre-of-pressure to one side while keeping the head central over the feet (the pelvis moves more to the side to counterbalance). This keeps the visual and vestibular systems ‘normally level’, and puts less demand on the righting reflex. It’s also an organization (a word I prefer to 'posture') that can be commonly observed in "standing at the bar" where the ground is level, and weight is on one leg but the head is central, AKA ‘hanging off the hip’ of the standing leg. Honestly; check it out next time you’re down the pub. Or anywhere where people are standing around.

So: if the relationship of the head with respect to gravity, horizon and the rest of the body wasn’t measured, how do we know which strategy was used to move the centre-of-balance? Could the participants have used a plank strategy on one side, and an articulated strategy on the other? This might be more interesting to explore than a postural relationship to a conceptual number line… but we don’t know because the data isn’t there. The same applies to the Miles et al study… To paraphrase Eric above: I'm not trying to be a jerk. I really believe that many of the problems with body-talk are about getting the descriptions accurate in profound ways :)

"So the paper itself is theoretically incoherent, yet another victim of psychology's lack of a central theory."

Would you not view behaviorism as a possible candidate for this spot? I've read a few of your articles and it seems (to me at least) that your general ideas on psychology are pretty compatible with the position espoused by the radical behaviorists.

I don't want to derail this topic by going into too much detail, but obviously behaviorism is one of the most misunderstood concepts in science and (from reading a few of your posts mentioning behaviorism) I think you may have fallen victim to some of these misconceptions which may be leading you to reject it before fully considering it. In your post wishing Skinner a happy birthday I noticed someone clarified that Skinner was against stimulus-response psychology, but it's also good to highlight the fact that he didn't reject internal states (only internal states that were not empirically justified) and behaviorism is not focused on animals (there are entire behaviorist journals dedicated to human studies).

I think Chomsky's review of 'Verbal Behavior' is a great demonstration of how behaviorism has been misrepresented, as most academics looking at the issue come to the conclusion that for Chomsky to have so severely misunderstood behaviorism, he must have never read a single book on the topic (including Skinner's work). There's a good article by MacCorquodale here, "On Chomsky's Review of Skinner's Verbal Behavior" (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1333660/), where he basically starts by apologising to Chomsky for nobody formally replying to him sooner, but the simple fact was that his article was so confused that nobody could figure out who or what he was trying to criticise.

In general I agree; I'm actually a fan of Skinner, and I have learned more that I like since I wrote that birthday post.

I am definitely essentially a behaviourist (Gibson considered himself one) but not quite in the Skinnerian mould - more the Holt/Tolman 'molar' behaviourism. Plus Skinner didn't have a decent theory of perception, so he had a limited understanding of the input organisms could take. But while I don't think Skinner's behaviourism was complete, I do like a lot about it, especially it's rigour and strong efforts to avoid making the psychologist's fallacy. I think that kind of empirical focus and discipline should feature prominently in any psychology.